Conversion of alkyl nitrates to carboxylic acids

ABSTRACT

ALKYL NITRATES ARE OXIDIZED WITH NITRIC ACID IN THE PRESENCE OF A VANADATE SALT AND AN NO2 OR NITRITE-CONTAINING INITIATOR TO YIELD CARBOXYLIC ACIDS CONTAINING VARYING NUMBERS OF CARBON ATOMS. SELECTIVITY AS BETWEEN THE CARBOXYLIC ACID TYPES PRODUCED IS ATTAINED BY SELECTIVE CONTROL OF THE TEMPERATURE AT WHICH THE NITRIC ACID OXIDATION IS CARRIED OUT.

United States Patent 3,770,782 CONVERSION OF ALKYL NITRATES TOCARBOXYLIC ACIDS Clyde E. Bishop, Indianapolis, Ind., assiguor toContinental Oil Company, Ponca City, Okla. No Drawing. Filed Dec. 30,1970, Ser. No. 102,909 Int. Cl. C0811 17/36 U.S. Cl. 260-413 7 ClaimsABSTRACT OF THE DISCLOSURE Alkyl nitrates are oxidized with nitric acidin the presence of a vanadate salt and an N0 or nitrite-containinginitiator to yield carboxylic acids containing varying numbers of carbonatoms. Selectivity as between the carboxylic acid types produced isattained by selective control of the temperature at which the nitricacid oxidation is carried out.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the production of carboxylic acids, and more particularly, tothe nitric acid oxidation of alkyl nitrates to yield a mixture ofcarboxylic acids of varying chain length.

Brief description of the prior art It is known that alkyl nitratesderived from, for example, the nitric acid esterification of alcohols,can be converted to carboxylic acids by hydrolizing the esters. Aprocess of this type is disclosed in Schoenbrunn U.S. Pat. 3,284,494.

Brief description of the present invention This invention provides aprocess for directly producing straight chain carboxylic acids froml-alkyl nitrates by oxidation of the alkyl nitrates with nitric acid inthe presence of a vanadate salt. The temperature of the reaction iscontrolled to selectively control the ratio of the several types ofcarboxylic acids yielded by the reaction. More specifically, thereaction is carried out at a temperature in the range of from about 20C. to about 110 C. using nitric acid having a strength which ispreferably from about 8 molar to about 21 molar. When the reaction iscarried out at relatively low temperatures within the operating range, apredominance of carboxylic acid containing the same number of carbonatoms as contained by the alkyl nitrate reactant is present in themixture of carboxylic acids produced by the reaction. When the reactionis carried out at relatively high temperatures within the range, thepredominant carboxylic acid produced is one containing one less carbonatom than the number of carbon atoms contained in the starting alkylnitrate.

An object of the invention is to provide a method for directly oxidizingalkyl nitrates to carboxylic acids.

Another object of the invention is to provide a method for selectivelyconverting alkyl nitrate to a mixture of carboxylic acids of varyingchain lengths.

Other objects and advantages of the invention will be apparent as thefollowing detailed description of the invention is considered.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Incarrying out the nitric acid oxidation of alkyl nitrates to producecarboxylic acids, nitric acid having a strength of from about 8 molar toabout 21 molar is employed. Preferably, the nitric acid has a strengthof from about 12 molar to about 16 molar. The akyl nitrates utilized inthe oxidation reaction are preferably straight chain l-alkyl nitrates. Avanadate salt promoter is utilized, and the reaction is carried out at atemperature in the range of from about 20 C. to about 110 C. A nitritecompound or N0 is preferably used as a reaction-initiator, and isparticularly effective when the reaction is carried out at relativelyhigh temperatures within the described temperature range. The reactiontime employed is from about 1 hour to about 4 hours, with a 2 hour totalreaction time being preferred.

We have determined that the selectivity obtained as between the severaltypes of carboxylic acids produced in the described oxidation reactioncan be controlled by control of the temperature utilized when carryingout the reaction. Thus, when the reaction is carried out at relativelylow temperatures (of from about 20 C. to about 60 C.) within thedescribed temperature range, carboxylic acids which contain the samenumber of carbon atoms as the alkyl nitrate starting materialspredominate in the mixture of carboxylic acids which is produced. When,on the other hand, a relatively high temperature (of from about 60 C. toabout 110 C.) Within the described range is employed, a mixture ofcarboxylic acids results from the oxidation, but in this case, thecarboxylic acid containing one less carbon atom than the total number ofcarbon atoms in the alkyl nitrate material predominates in the product.Moreover, an increase in the amount of carboxylic acid containing twocarbon atoms less than the carbon atom content of the starting materialis also preceived to occur.

The following examples will serve to further illustrate the principlesof the invention, but are not intended to be comprehensive statements ofall the possible reactants or reactant conditions and parameters whichmay be employed in carrying out the process of the invention.

EXAMPLE 1 500 ml. of 15.4 molar nitric acid, 0.23 gram of ammoniumvanadate and 6.9 grams of sodium nitrite were charged to a three-necked,round-bottom flask equipped with a condenser, thermometer, mechanicalstirrer and addition funnel. The reaction mixture was then heated to C.,and 17 grams of octyl nitrate were then added to the reaction flask in adrop-wise fashion by the use of the addition funnel. The addition of theoctyl nitrate was carried out over a period of 25 minutes. The reactionwas then continued for a total period of two hours as measured from thestart of the addition of the octyl nitrate to the flask.

A portion of the product mixture was then isolated by extraction withpentane, and the carboxylic acids extracted from the pentane solutionwith base. After treatment of the base solution with a mineral acid tofree the carboxylic acids, the carboxylic acids were analyzed byaddition of decanoic acid as an internal standard, followed byesterification and quantitative analysis of the esters by gaschromatography.

It was determined that 12.83 grams of the carboxylic acids were producedby the reaction, and that the product mixture contained 0.26 gram ofneutral material which was found to be the octyl nitrate startingmaterial. Analysis of the mixture of carboxylic acids showed the mixtureto contain 8.21 weight percent of octanoic acid, 74.53 weight percent ofheptanoic acid, and 4.39 weight percent of hexanoic acid.

EXAMPLE 2 A reaction flash equipped in the same way as described inExample 1 was charged with nitric acid, ammonium vanadate and sodiumnitrite in the same quantities as described in Example 1. The reactionmixture was then heated to 40 C., and 16.68 grams of octyl nitrate wereadded drop-wise through the addition funnel. The reaction was thenallowed to continue at 40 C. for a total reaction time of two hours, asmeasured from the time at which addition of the octyl nitrate wasstarted.

After working up the product mixture in a manner described in Example 1,and completing analyses of the product mixture for carboxylic acids andneutral material, it was found that the product mixture contained atotal carboxylic acid content of 5.55 grams. 10.35 grams of neutralmaterial were produced, and this material was shown to be the startingoct'yl nitrate. The weight percent distribution of carboxylic acids inthe product was 63.9 weight percent of octanoic acid, 27.9 weightpercent of heptanoic acid, and 1.39 weight percent of hexanoic acid.

EXAMPLE 3 To a reaction flask fitted out in the manner described inExample 1 and containing 500 ml. of 15.4 molar nitric acid, 0.004 moleof ammonium vanadate and 2.4 mole of N were added. After heating thecontents of the flask to C., 47.09 grams of octyl nitrate were addeddropwise through the addition funnel. Heating of the reaction mixturewas continued for a total reaction period of two hours. The product wasworked up and analyzed and found to contain 0.45 gram of carboxylicacids and 45.6 grams of unreacted octyl nitrate. Of the carboxylic acidsproduced, 90.4 Weight percent was octanoic acid and 4.7 weight percentwas heptanoic acid.

EXAMPLE 4 To a reaction flask, made up with accessories as described inExample 1, 500 ml. of 15.4 molar nitric acid, 0.004 mole of ammoniumvanadate and 2.4 mole of nitro gen dioxide were added. The temperatureof the flask and its contents was then elevated to 60 C. and 47.1 gramsof octyl nitrate were added in drop-wise fashion. After a total reactionperiod of one hour, the reaction was terminated and the contents of theflask allowed to cool. The products of the reaction were then worked up,separated and analyzed. A total amount of 26.1 grams of carboxylic acidswere produced by the reaction, and 10.5 grams of neutral octyl nitratewere found in the reaction product mixture. The mixed carboxylic acidswere found to contain 45 weight percent of heptanoic acid and 53.2weight percent of octanoic acid.

From the foregoing description of the invention, it will have becomeapparent that mixed carboxylic acids, in which the distribution of htevarious acids within the mixture is controlled by control of thetemperature at which the reaction is run, can be effectively produced byoxidizing alkyl nitrates, utilizing nitric acid as the oxidant. Althoughvarious reaction conditions have been herein described, and illustrativereactants have been set forth, it is to be understood that variouschanges and innovations can be made in the described reaction conditionsand reactants without departure from the basic principles of theinvention. Changes and innovations of this type which do not depart fromthe basic principles of the invention are therefore deemed to becircumscribed by the spiritand scope of the invention except as the samemay be necessarily limited by the appended claims or reasonableequivalents thereof.

What is claimed is:

1. A method for producing straight chain l-alkane carboxylic acidscomprising oxidizing straight chain l-alkyl nitrates with nitric acid inthe presence of a vanadate salt at a temperature of from about 20 C. toabout 110 C.

2. The method defined in claim 1 wherein a reaction initiator selectedfrom the group consisting of a nitrite compound and N0 is added to thereaction mixture.

3. The method defined in claim 1 wherein the reaction is carried out ata temperature of about 20 C. to about C. to produce a mixture ofstraight chain l-alkane carboxylic acids in which the carboxylic acidcontaining a number of carbon atoms equal to the number of carbon atomsin the straight chain l-alkyl nitrate starting material predominates.

4. The method defined in claim 1 wherein the reaction is carried out ata temperature above 60 C. to thereby substantially increase the yield ofstraight chain l-alkane carboxylic acids containing fewer carbon atomsthan the straight chain l-al-kyl nitrate starting material.

5. The method of producing straight chain l-alkane carboxylic acidscontaining fewer than x number of carbon atoms which comprises heating amixture of a straight chain l-alkyl nitrate containing at carbon atoms,nitric acid having a strength of from about 12 molar to about 16 molar,a vanadate salt, and a nitrite salt to a temperature exceeding 60 C. fora period of about two hours.

6. The method defined in claim 5 wherein said mixture is heated to atemperature of at least C. for said period.

7. The method defined in claim 5 wherein 15.4 molar nitric acid isemployed.

References Cited UNITED STATES PATENTS 3,704,319 11/1972 Washechec-k etal.

260-413 X R 3,715,394 2/1973 Boichard et al. 260535 R 3,284,494 11/1966Schoenbrunn 260533 2,862,942 12/ 1958 Snyder 260-413 FOREIGN PATENTS559,599 7/1958 Canada 260531 LEWIS GOTTS, Primary Examiner E. G. LOVE,Assistant Examiner US. Cl. X.R. 260531, 540

